Various decoupling arrangements are known from "Signal & Wire", 71 (1979) 5, pages 94 to 100. They basically consist of two parallel resonant circuits tuned to different frequencies which usually operate as a transmitting circuit and a receiving circuit, respectively. The cross bonds interconnecting the rails serve as compensating elements for the traction power return. If a number of such decoupling arrangements are disposed in the track at predetermined intervals, the transmitting circuit of each decoupling arrangement will work into the receiving circuit of the next decoupling arrangement. In this manner, a chain of adjoining track circuits is obtained, which makes it possible to monitor the track for unoccupancy and occupancy nearly without a gap. Each axle which is located between two decoupling arrangements and short circuits the two rails of the track will be detected by a fall of the voltage in the receiving circuit of the next decoupling arrangement below a predetermined threshold value due to the short circuit. Only if simple shorting bonds are used as cross bonds will narrow monitoring gaps remain in the immediate vicinity of the cross bonds, where a single axle will not be detected.
The inductances in the parallel resonant circuits of the decoupling arrangements are provided by parts of the rails and of the cross bonds, while the capacitances are provided by capacitors which are located outside the track in so-called tuning units and are connected to given points of the rails and/or of the cross bonds via separate leads.
These known arrangements have the disadvantage of necessitating critical tuning in the track and, consequently, showing an extremely complicated tuning behavior. Also, subsequent detuning of the resonant circuits is quite possible and greatly affects the curves showing the influence exerted by passing axles.
The object of a decoupling arrangement of the above kind is to permit an electrical division of a continuous welded track into track sections and fail-safe monitoring of these track sections for unoccupancy and occupancy.